The subject carbon canisters of the present invention relate to the capture and purging of hydrocarbon vapors as air is drawn into an underground storage tank and released therefrom, such as during fueling by ORVR vehicles and when fuel is delivered to the underground storage tank.
Fuel storage tanks, such as underground storage tanks, UST, used to store fuel at gasoline dispensing facilities or GDF, are subject to variable pressures that affect the ability of the fueling system and vapor recovery system to operate correctly. The fuel storage tanks thus have one or more vents which release the excess pressure when the tank exceeds a predetermined maximum pressure. Excess pressure can be caused by vacuum assisted refueling when more vapors are drawn into the tank than volume of fuel dispensed, by not connecting the vapor return hose to the transfer tank when refueling the tank, or by local atmospheric conditions, particularly barometric pressure changes associated with weather. Additionally, negative pressure, or partial vacuums, can appear in the storage tank by dispensing more fuel than vapors that are drawn into the tank as during vacuum assist, or balance system, refueling. In that situation, the tank requires additional pressure, or, more likely, the vacuum must be dissipated.
Since the 1998 automotive model year, onboard refueling vapor recovery, ORVR, technology has been employed, initially on passenger cars and presently on light trucks. As is well known, the motorist refuels a vehicle at a service station. The fuel is pumped from an underground tank, by the dispenser, through a hose and nozzle, for filling the vehicle fuel tank. Normally, the vapors generated within the fuel tank, through refueling, are returned through the vapor path of the fuel hose, back to the dispenser, either by the balanced pressure method—called Stage II vapor recovery—or by a pump, and then are returned to the underground storage tank for containment.
Escaped gasoline vapors raise pollution concerns and trigger governmental regulations. Hydrocarbon vapors, such as octane, under the action of sunlight form ground level ozone. Such ozone affects the respiratory tract in humans. Normally, balance type Stage II vapor recovery stations operate at a negative pressure except during closure of the station. When an ORVR equipped vehicle is refueled, the ORVR system retains the vapors from the vehicle fuel tank, and does not return the vapors to the dispensing system, often lowering the pressure within the fuel storage tank. An ORVR vehicle refueling at a Stage II equipped station imposes a negative pressure on the Stage II system that draws some atmospheric air into an underground fuel tank. The atmospheric air then absorbs hydrocarbon vapors released from stored fuel, and with each ORVR vehicle that refuels the pressure in the underground tank decreases. When that pressure exceeds a limit, valves release the air containing hydrocarbons from the tank to the atmosphere, thus contributing to pollution when attempting to avoid it.
Generally, various methods are employed to capture gasoline vapors and then return them to the underground tank. The vapor recovery systems, in doing so, prevent vapors from escaping to the atmosphere as components of pollution. Vapor recovery systems are of two types. First, the vacuum assist system utilizes the partial vacuum created within the nozzle, by means of the flowing fuel passing through the nozzle during its dispensing, or a vacuum pump, and this partial vacuum tends to attract vapors back into the nozzle, either through a bellows arrangement used in conjunction with the nozzle spout, or through a passage created between concentrically arranged nozzle spouts, that allows the partial vacuum to attract the vapors back into the spout for return to the underground storage tank. Second, the balanced pressure system begins upon pumping gasoline into an automobile fuel tank, and then displaced vapors are forced back towards the emplaced nozzle that captures gasoline vapors for return back into the vapor line and eventually to the underground storage tank.
Prior art designs defeat pressurization and vapor absorption in the underground fuel tank by two classes of devices. First, nozzles and other parts of the dispensing system are regulated by an ORVR detecting sensor. The sensor recognizes the pressure dip caused by an ORVR vehicle and promptly reduces air ingestion to less than the volume of fuel dispensed. The sensor and nozzles result in a slight negative pressure in the underground tank that limits vapor loss to the atmosphere. Second, membranes and condensing processes control the vapor at the source, in the underground fuel tank. The membranes and condensing processes cool or otherwise liquefy gasoline vapors and return them to the underground tank while letting cleansed air return to the atmosphere. Though collecting vapors, the prior art required additional mechanical equipment, and has higher installation and operational costs, and; energy consumption.
The patent to Healy, U.S. Pat. No. 5,305,807, describes a vapor recovery device. This device has a vacuum pump connected to underground storage tanks coupled with a solenoid. A pressure switch monitors pressure in the UST and energizes the solenoid to move valves within three conditions to direct air flow into or out of the UST. The valves control flow of hydrocarbons and air through a conduit system. This patent discloses a pump and solenoid not in the present invention.
Additionally, the California Air Resources Board “CARB” has imposed Enhanced Vapor Recovery upon equipment used at gasoline dispensing facilities. The Assignee has developed an activated carbon canister with an internal pressure control system for a UST. The internal pressure control system goes by the name of a vapor processor according to CARB. In a typical UST, a pressure vacuum valve vents the pressure and hydrocarbon emissions from a UST when the pressure reading exceeds 2.5 inches of water. However, some vapor processors can release hydrocarbons at pressure exceeding 0.25 inches of water. The order of magnitude reduction in pressure has concerned CARB that more hydrocarbons will be emitted by vapor processors and that the pressure vacuum valves will be bypassed and no longer serve their function at suitable pressure levels. Additionally, CARB seeks the pressure vacuum valve to operate in the event of a vapor processor failing. Existing vapor processors do not provide a mechanism or method to transfer pressure control from the vapor processor back to the pressure vacuum valve.
The present art overcomes the limitations of the prior art. That is, at least one form of the present invention, a canister of activated carbon with a valve actuated by the weight of saturated carbon, provides a mechanical closing of an inlet valve returning pressure control to the pressure vacuum valve. Such form of the present invention returns pressure control before or when it is saturated with hydrocarbon vapors thus allowing the pressure vacuum valve to regulate hydrocarbon vapors that accumulate before or beyond saturation at less than 2.5 inches of water pressure.
Thus, prior art devices do not provide for storing purged hydrocarbon vapors within a container and preventing their return into an underground fuel tank while allowing air to pass freely through the container. At least one form of the present invention, hereinafter often referred to as the Stage II form of the invention, uses the heavier weight of carbon saturated with hydrocarbons as an input to close a valve. Such form of the present invention does not require electrical power or an external control to actuate.
The form of the invention more particularly directed to Stage I vapor recovery, such as when the storage tank is being filled with fuel, such as from a tank truck, unlike the Stage II form, does not require a valve activated by weight of the saturated carbon to affect the capture and purging of hydrocarbons. Like the Stage II form, such Stage I form employs a carbon canister, but the canister is designed to be free breathing and includes a surge protection device to prevent high flow rates through the canister in case an improper fuel delivery is made, but no weight activated valve. Such form can therefore be viewed in many regards as a simplified or stripped down form of the Stage II form, but a form that nevertheless operates effectively in Stage I recovery systems to efficiently capture and purge hydrocarbons from the air passing through the canister as fueling operations occur. Such Stage I form is particularly appropriate for use at service stations without Stage II vapor recovery.